The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An airplane is moved by several turbojet engines each housed in a nacelle also housing a set of related actuating devices connected to its operation and performing various functions when the turbojet engine is operating or stopped. These related actuating devices in particular includes a mechanical thrust reverser actuating system.
A nacelle generally has a tubular structure comprising an air intake upstream of the turbojet engine, a middle section designed to surround a fan of the turbojet engine, a downstream section designed to surround the combustion chamber of the turbojet engine and optionally incorporating thrust reverser means, and generally ends with a jet nozzle, where of the outlet is situated downstream from the turbojet engine.
Modern nacelles are designed to house a dual flow turbojet engine capable of generating, by means of the rotating fan blades, a hot air flow (also called primary flow) from the combustion chamber of the turbojet engine, and a cold air flow (secondary flow) that circulates outside the turbojet engine through an annular passage, also called the stream, formed between the fairing of the turbojet engine and an inner wall of the nacelle. The two flows of air are discharged from the turbojet engine through the rear of the nacelle.
A nacelle generally comprises an outer structure, called an outer fixed structure (OFS), which defines, with a concentric inner structure of the rear section, called an inner fixed structure (IFS), surrounding the structure of the turbojet engine strictly speaking behind the fan, an annular flow channel, also called secondary stream, serving to channel a cold air flow, called secondary, that circulates outside the turbojet engine.
The role of the thrust reverser is, during the landing of an airplane, to improve the braking capacity thereof by reorienting at least part of the thrust generated by the turbojet engine forward. In that phase, the reverser obstructs the stream of the cold flow and orients the latter toward the front of the nacelle, thereby generating a counter-thrust that is added to the braking of the wheels of the airplane.
The means used to perform this reorientation of the cold flow vary depending on the type of the reverser. However, in all cases, the structure of a reverser comprises movable cowls that can be moved on the one hand between a deployed position in which they open a passage in the nacelle intended for the deflected flow, and on the other hand a retracted position in which they close that passage. These cowls can perform a deflection function or simply serve to activate other deflection means.
In the case of a cascade reverser, also known as a cascade thrust reverser, the reorientation of the air flow is done by the cascade vanes, the cowl having only a simple sliding function aiming to expose or cover the vanes. Complementary blocking doors, also called flaps, activated by sliding the cowl, generally allow closing of the stream downstream from the vanes so as to optimize the reorientation of the cold flow.
These flaps are mounted pivotably, by an upstream end, on the sliding cowl between a retracted position, in which, with said movable cowl, they ensure the aerodynamic continuity of the inner wall of the nacelle, and a deployed position in which, in a thrust reversal situation, they at least partially obstruct the annular channel so as to deflect a gas flow toward the cascade vanes exposed by the sliding of the movable cowl. The pivoting of the flaps is guided by control rods connected on the one hand to the flap, and on the other hand to a fixed point of the inner structure defining the annular channel.
In order to offset certain problems related to the driving of these blocking flaps as well as aerodynamic disruptions that the control rods passing through the stream generate, thrust reverser devices have been proposed with no control rod passing through the air circulation stream.
Reference may in particular be made to application FR 2,907,512 as well as application FR 09/53630, not yet published, describing such thrust reversers.
It will be noted that the blocking flap can, in the direct jet position, ensure the inner continuity of the moving cowl and form a wall of the circulating stream or be retracted inside said moving cowl. The latter solution makes it possible to further reduce surface accidents in the circulation stream and increase the inner surface of the moving cowl that can be acoustically treated. Such a device is in particular shown in document EP 1,843,031. The use of blocking flaps completely retracted inside the moving cowl allows a significant reduction in the drag and mass of the assembly, and consequently, a decrease in fuel consumption and improved acoustic performance.
Furthermore, the opening of the flap must respect certain kinematics relative to the opening kinematics of the moving flap and activation of the vanes.
More specifically, the opening kinematics of the blocking flaps must make it possible to disrupt the air pressure in the stream, and more generally in the nacelle, as little as possible so as to reduce disruptions in the air flow and their impact on the operation of the turbojet engine.
More specifically, the air discharge cross-section of the turbojet engine must preferably be kept substantially constant.
Thus, if the blocking flaps are deployed too soon, in particular before the reverser passage has been opened through the nacelle, the air discharge cross-section will be smaller than the discharge cross-section normally available in direct jet, which will result in a significant and sudden increase in the air pressure in the stream of the turbojet engine before the passage is completely open and the normal circulation pressure has been reestablished.
Reciprocally, if the blocking flaps are deployed too late, then the reverser passage cross-section is added to the available direct jet cross-section, the total discharge cross-section then being larger than the normal direct jet discharge cross-section, which results in a pressure drop.
In the case of blocking flaps that can be retracted inside the moving cowl, a slight delay should also be provided in their deployments so that they do not abut in an upstream end of the moving cowl.
The presence of control rods passing through the stream and connected to an inner fixed structure according to the prior forms makes it possible to resolve this type of problem relatively easily.
In any case, so as to be able to pivot, the blocking flap can be connected on the one hand to a stationary part, and on the other hand to a moving part.
In the cases of the prior forms with control rods passing through the stream, the moving part is generally the moving cowl and the stationary part is therefore the inner fixed structure.
The potential attachment surface offered by this inner fixed structure is relatively large, and therefore allows relatively precise and satisfactory control of the opening kinematics. More specifically, depending on the desired kinematics, it will easily be possible to connect the control rods slightly further upstream or slightly further downstream on the inner fixed structure and through the stream so as to cause slightly different opening and closing kinematics.
Furthermore, due to the substantially cylindrical shape of the nacelle, the flaps can be made to overlap slightly in the open position. It should therefore be ensured that the adjacent flaps indeed have very slightly different opening and closing kinematics so as to ensure that the adjacent flaps overlap correctly and do not collide.
Such kinematics are difficult to implement for flaps without control rods passing through the stream, since the choice of their attachment points is considerably more reduced than on the inner fixed structure.
In cases of thrust reversers without control rods in the stream, the moving part to which the flap is connected to pivot remains the moving cowl, and the choice of its stationary part is, however, more limited, and it may in particular be a front frame of the reverser vanes. The small space available inside the moving cowl should also be taken into account.
It is therefore understood that it will be difficult to place the attachment point slightly further upstream or slightly further downstream as a function of the desired kinematics.
Furthermore, the development of thrust reverser devices has also made it possible to implement thrust reverser devices suited to nacelles with a very high bypass ratio having a relatively short downstream section relative to the cascade vane length necessary to reverse the flows they generate.
Such thrust reverser devices, for example as described in application US 2010/0212286 as well as the as-yet unpublished application FR 10/56006, provide for the implementation of cascade vanes that are at least partially retractable into the thickness of the adjacent middle section.
Such systems make it possible to reduce the length of the downstream section, and therefore the drag of the nacelle.
One problem with these systems is their compatibility with the aforementioned thrust reverser technology with no control rod passing through the stream.
First, the front frame of the cascade vanes no longer constitutes a stationary point for connecting the blocking flaps.
Furthermore, the deployment kinematics of the vanes and flaps are very different. That is why document US 2010/0212286 keeps the system of connecting rods passing through the air circulation stream.
Thus, the production of the thrust reverser device with no control rods driving the blocking flaps passing through the stream and with retractable vanes requires a particular form, the solution of which is the subject-matter of this application.